1. Field of the Invention
The present invention relates generally to an image reading unit and an information processing apparatus, and more particularly to an image reading unit suitable for reading a photograph printed on printing paper, and an information processing apparatus such as a scanner, a facsimile machine, a copying machine and a printer that include the image reading unit.
2. Description of Related Art
A conventional image reading unit shown in FIG. 14 has a casing 10, which extends in a direction perpendicular to paper, and the casing 10 contains a line sensor 12, a SELFOC.RTM. lens 14, red, green and blue light emitting diodes (LED) 16, and a light transmission tube 18. A plate glass 20 closes the casing 10.
A scanner using the above-mentioned image reading unit is provided with a transport roller (not shown) that presses a subject-sheet 1 tightly between itself and the plate glass 20. The rotation of the transport roller transports the subject-sheet 1 on the surface of the plate glass 20.
The LEDs 16 emit red, green and blue illumination light sequentially, and the illumination light is transmitted to a predetermined image reading area of the image reading unit through the light transmission tube 18 and the plate glass 20. The illumination light falls on the subject-sheet 1, and the light that is reflected by the subject-sheet 1 in the image reading area is formed on a light receiving surface of the line sensor 12 through the SELFOC.RTM. lens 14. The line sensor 12 converts the formed image into line-sequential signals of the three colors: red, green and blue.
The scanner including the conventional image reading unit has a disadvantage of poor transportability of the subject-sheet that has a smooth surface, since the adhesion of the surface of the subject-sheet to the surface of the plate glass, which operates as a subject-sheet receiving face of the image reading unit. If the subject-sheet is the photograph printed on printing paper in particular, a gelatinous layer on the surface of the photograph absorbs moisture under the high humidity and temperatures and raises the adhesion of the subject-sheet to the plate glass.
Moreover, the conventional image reading unit has a shortcoming in that optical interference, which makes noise in the read image, occurs between a light reflected on the glass surface and a light reflected on the subject-sheet surface, since the subject-sheet surface is in contact with or extremely close to the plate glass surface in the image reading area.